The present invention relates to wireless digital networks, and in particular, to the problem of sensing orientation of wireless access nodes and/or wireless antennas.
Modern wireless digital networks typically consist of one or more access nodes connected to a controller, and typically provide services to wireless clients according to IEEE 802.11 standards. Particularly with access nodes featuring one or more built-in antennas, differences in mounting and orientation may have significant effects on coverage and signal strength. Additionally, when two access nodes are linked together, antenna orientation and polarization should be the same.
Indoor access points, particularly those with integrated antennas, typically have two primary installation methods: wall mounted, or ceiling mounted. The differences in resulting antenna height and polarization between different mounting types and orientations may result in significant differences in coverage and signal strength.
In the case of a typical omnidirectional antenna, such as a dipole radiator, the free-space radiation pattern produced is similar to a donut, with the maximum radiation broadside to the dipole elements, and minimal radiation off the ends of the dipole elements. As an access node using such antennas is changed from a horizontal mounting orientation, such as mounted on a ceiling, to a vertical orientation such as a wall mount, the minima and maxima of antennas within it also change, as does the polarization of the electric field.
For example, a wall mounted access node can be designed to have an omnidirectional dipole antenna element that is vertically oriented with respect to the floor. This will produce a donut-shaped free-space radiation pattern with the body of the donut parallel to the floor as shown in FIG. 1. In this case the polarization of the electric field is also vertical with respect to the floor.
If this same access node is then installed on the ceiling without any mechanical change (i.e. articulating the antenna down), the free-space pattern will then be a vertically oriented donut as shown in FIG. 2 with a vertical electric field and a radiated pattern which is significantly different.
Similarly, when a pair of access nodes are used for example to provide a wireless point-to-point bridge between two locations, it is important that the antennas at both ends of the bridge have the same orientation and polarization to maximize received signal strength at both ends. If for example one node is installed with a vertically polarized antenna and the other node is installed with a horizontally polarized antenna, significant signal loss will result.
Because the orientation of the access node and its antenna or antennas affect signal strength and coverage, a way to sense the orientation of an installed access node and/or its antennas is desirable.